The present invention relates to a heat sealable wrapping or packing film which is capable of forming a peelable seal and which exhibits good optical qualities. The seal is achievable either between two films of this kind or between one film of this kind and another wrappable packing film of any other kind without affecting optical qualities.
A peelable seal is defined to be the seal or joint between two films produced by heat sealing or impulse sealing, the joint thus formed having the property of being able to open in the original plane of joining of the two films by the action of a pulling force, without wrenching off or tearing occurring in the material of the two films used to make up the joint. For the purposes of the present invention, the peelable seal must possess a mechanical resistance sufficient to maintain the wholeness and the tight-seal properties of the packing and wrapping during storage and transport until such time as the packing or wrapping is opened by the user of the article. The mechanical resistance of the peelable seal must be low enough to permit ready manual opening of the joint, i.e., without the use of any auxillary instrument.
In addition, the film used for wrapping or packing of cqrtain commercial products must exhibit good optical qualities, such as low percent haze. Foodstuffs, for example, fruit, vegetables, meat and the like necessitate a wrapping or packaging of very transparent films, as do medical and surgical products.
In the past, many varieties of thermoplastic materials have been employed in the manufacture of films capable of forming peelable seals. See, for example, U.S. Pat. No. 4,189,519, which discloses a blend for producing a peelable heat seal comprising about 50 to 90 percent by weight of a copolymer of about 80 to 96 percent by weight ethylene and about 4 to 20 percent by weight of an ethylenically unsaturated ester and about 10 to 50 percent by weight of a crystalline isotactic polybutylene. While a peel seal patent, the film of '519 does not exhibit the low percent haze values characteristic of a film with good optics.
U.S. Pat. No 3,900,534 discloses thermoplastic shrink films with good heat seal characteristics and good optical properties, however, '534 does not address the need for a peel seal film which also has good optics.
There has been a long felt need for a wrapping or packing material having easy peelability at the seal and yet which possesses good optics which results in a transparent film for meat and other articles where it may be necessary or desirable for the consumer to clearly see the wrapped product.